|Table of Contents
Barrett, R.P., T. Mebrahtu, and J.W. Hanover. 1990. Black locust: A
multi-purpose tree species for temperate climates. p. 278-283. In: J. Janick
and J.E. Simon (eds.), Advances in new crops. Timber Press, Portland, OR.
Black Locust: A Multi-purpose Tree Species for Temperate Climates*
Robert P. Barrett, Tesfai Mebrahtu, and James W. Hanover
- MULTIPLE USES
- RESEARCH AT MICHIGAN STATE UNIVERSITY
- Biomass Trials
- Genetic Variation and Breeding
- Wood Chemistry
- Green Biomass for Forage
- Fig. 1
- Fig. 2
- Fig. 3
- Fig. 4
- Fig. 5
Black Locust (Robinia pseudoacacia L.) is a nitrogen-fixing legume,
native to southeastern North America and now naturalized extensively in the
temperate regions of North America, Europe, and Asia. This tree is useful but
underutilized for lumber, poles, wood fiber, land reclamation, beekeeping, fuel
and forage. It grows very rapidly survives droughts and severe winters,
tolerates infertile and acidic soils (Miller et al. 1987), and produces
livestock feed nutritionally equivalent to alfalfa (Medicago sativa L.)
(Baertsche et al. 1986). Commercial feed production, as silage, hay or leaf
meal, appears feasible.
Current research at Michigan State University began in 1978 with evaluations
for biomass production. Two provenance/progeny tests of over 400 families from
the natural and naturalized range in the eastern United States and Canada were
established in 1985 (Miller et al. 1987). Advanced generation breeding and
additional progeny tests are underway, and field trials are testing the effects
of seed sources, planting densities, harvest heights, and harvest dates on
The primary use of black locust wood has been for fence posts which, due to
flavonoids in the heartwood, can endure for over 100 years in the soil. The
lumber is one of the heaviest and hardest in North America, but the supply is
limited due to damage from the locust stem borer, Megacyllene robinae
(Miller et al. 1987). In Hungary, where the insect is not a problem, black
locust is a major timber tree (Keresztesi 1988) (Fig. 1).
The wood is suitable for chemical pulping systems in the paper industry, and
small amounts are presently being used in Michigan (Miller et al. 1987), where
the Menasha Corporation established a test plantation in 1988.
Widely used for erosion control and reforestation, black locust is ideally
suited for woody biomass plantings, and commercial energy production may
eventually become one of its primary uses in the U.S. Its virtues include
nitrogen fixing ability, inexpensive propagation by seed, rapid vegetative
propagation, adaptability to a wide range of site conditions, rapid juvenile
growth, high heat content of the wood, and prolific regrowth after cutting
(Miller et al. 1987).
In Hungary, black locust plantings are vital to commercial honey production
(Keresztesi 1988). The showy white pea-like flowers are borne on new growth
three to four weeks after growth begins. Vigorous specimens can bloom in three
years from seed, much earlier than most trees (Fig. 4).
The leaves are used for livestock feed in the Republic of Korea and in Bulgaria
(Keresztesi 1983, 1988). In the highlands of Nepal and northern India, where
black locust is naturalized, it is an important fodder tree. Branches above
the reach of livestock are cut when other green for-ages are scarce, and the
wood is used later for fuel.
Ground black locust tops including woody stems, from first and second harvests,
were found to be comparable to alfalfa (Medicago sativa L.) with 23-24%
crude protein, 7% lignin, and 4.2 kcal/g. Ruminal digestion by cattle was also
equivalent (Baertsche et al. 1986). When planted at close spacings, the new
growth can be harvested with conventional farm machinery for silage or hay
(Fig. 2, 3). The compound leaves can be separated and ground for a
high-protein ingredient of commercial feeds. Because black locust thrives on
sites too marginal for alfalfa, it merits further study as a forage crop.
In 1978, 24 tree species and hybrids were established in nine plantations
throughout Michigan. Those found most suitable for short rotation woody
biomass use were included in a second set of trials in 1983. Unlike the
others, black locust grew well at all sites, and it produced the most biomass.
Crown closure was observed in two years, greatly reducing the expense of weed
control compared with other trees. The species appears to reach the limit of
its productive range where the frost-free growing season is under 100 days
(Miller et al. 1987), although it does thrive in Michigan's upper peninsula.
The first breeding work began in Hungary in 1930, and many improved cultivars
for specific uses have been registered (Keresztesi 1983). Since 1983,
comprehensive germplasm collections of half-sib families (related by the seed
parent only) from the natural and naturalized range in the eastern U.S. and
southeast Canada have been made at Michigan State University and the University
of Georgia. First year data showed no trends due to geographic origin in any
of the traits measured: height, thorn length, number of leaders, winter
dieback, and times of leaf initiation and drop (Miller et al. 1987, Kennedy
1983). Michigan State University has about 800 clonal and seed accessions,
with 412 planted in two provenance/progeny tests in southern Michigan in 1985
In both plantations, survival averaged 82% one year after planting. At one
year, mean height was 126 cm, with a range from 34 to 290 cm. Length of the
stipular thorns ranged from 1 to 26 mm. Winter dieback ranged from 0 to 100
cm, averaging 6.6 cm, and the mean number of leaders was 2.3, ranging from 1 to
9. Stem diameter meter at 15 cm height averaged 3.1 cm, ranging from 0.3 to
11.4 cm. Twig borer attack, diameter, and times of budbreak and leaf
initiation were also measured. All traits showed family differences, but no
variation by region of origin was found. After five growing seasons some trees
have surpassed 600 cm in height.
Analysis of variance for six traits indicated highly significant (P = 0.01)
family differences. Family x site interactions were non-significant except for
dieback which removes the need for separate breeding programs for different
sites (Mebrahtu and Hanover 1989).
Individual tree and family heritabilities for height growth were high, and
comparable to other tree species. Although heritabilities may change from year
to year, a gain of up to 50% of the mean height is possible after one
generation of interbreeding the best 40 individuals. This is high compared to
other tree species.
A progeny test of 44 new families and 11 families from the previous tests was
planted at three Michigan sites in 1989. Seeds were collected from trees that
bloomed in 1987 at four years from seed, and the seedlings were planted in the
field in 1988. Superior individuals have been reproduced from stem and root
cuttings, and established in plots of single clones. These will be used for
seed production and forage/biomass studies.
Black locust wood is being studied to find the chemical basis for its
remarkable decay resistance. High flavonoid concentrations (6% of dry weight)
are important, especially the constituents robinetin and dihydrorobinetin
(Smith et al. 1989). When impregnated into easily decayed woods, heartwood
extracts have raised decay resistance to a level equivalent to that attained by
commercial wood preservatives (Smith et al. 1989).
Two field trials are being conducted to test the effects of seed sources on
forage yield (Fig. 3). Plots of mixed seed from average local trees are
compared with plots of five rapid growing families identified in the progeny
test, at densities of 40,000 and 250,000/ha. Long term monitoring of
reproduction, survival and wields of these plots, with continued biannual
harvest and no added fertilizer, will show whether black locust is suitable as
a perennial forage crop. In the other trial mixed local trees were compared
with plots of five families selected for extremely low or high numbers of
leaders, at densities of 250,000 and 500,000/ha. When harvested at 10 cm 60
days after sowing almost all trees had single stems. Doubling the density
raised average yield from 342 to 469 g/m2 dry weight.
In another trial five planting densities from 40,000 to 1,000,000/ha with
harvest heights of 5 and 20 cm were compared to determine how height affects
optimal density (Fig. 3). In 1988, dry weight yield increased with density
when cut at 20 cm. Yield was similar for the highest densities when cut at 5
cm, but such plots had very poor winter survival.
The relation between first and second harvest dates and total yields will be
investigated starting in 1989. Future tests will compare sexually and
vegetatively propagated plants from superior families and individuals, as
sufficient seeds and clones become available.
Field trials to compare yields of 4 traditional forage crops with black locust
were sown in 1989, at sites in the upper and lower peninsulas of Michigan.
Black locust can be vegetatively propagated from shoot and root cuttings, but
success rates vary among clones. Grafted or rooted shoot sections produce
lateral growth, while sprouts from roots grow upright (Prentice 1987). Tissue
culture has been accomplished from various plant organs (Davis and Keathley
1987) (Fig. 5), but presently it costs more than using cuttings. Improved seed
is not yet available commercially, but generic seed is quite cheap ($6/lb. for
about 60,000 seeds).
Black locust is suitable for many purposes. As one of the most adaptable and
rapid-growing trees available for temperate climates, it will always be valued
for erosion control and reforestation on difficult sites. Vast new forests of
rapid-growing species may be needed to slow the accumulation of CO2 in our
atmosphere. Energy from woody biomass will be more important in the future
when burning fossil fuels is reduced, either to preserve the global ecosystem
or simply due to rising costs. Breeding for straight stems and resistance to
borer insects could make black locust as valuable a timber tree in North
America as it already is in Europe. New cultivars with a longer blooming
season could become important for beekeeping and ornamental purposes. Many new
uses such as paper pulp, industrial chemicals, and livestock feed appear
promising. More are likely to be discovered with continuing research.
For the foreseeable future, direct seeding appears the most economical method
for establishing very dense stands for biomass, chemical extraction, or forage.
Seedling transplants are economical with wider spacings for soil conservation,
biomass, and timber uses. Cloning is now done by traditional vegetative
propagation methods, but advances in issue culture techniques could make these
obsolete, and greatly expand black locust production for all of its many uses.
- Baertsche, S.R, M.T. Yokoyama, and J.W. Hanover. 1986. Short rotation, hardwood
tree biomass as potential ruminant feed-chemical composition, nylon bag ruminal
degradation and ensilement of selected species. J. Animal Sci. 63:2028-2043.
- Davis, J. M. and D.E. Keathley 1987. In vitro propagation of mature black
locust (Robinia pseudoacacia L.). Plant Cell Rpt. 6:431-434.
- Kennedy, J M., Jr. 1983. Geographic variation in black locust (Robinia
pseudoacacia L.). MS Thesis, Univ. of Georgia, Athens.
- Keresztesi, B. 1983. Breeding and cultivation of black locust, Robinia
pseudoacacia, in Hungary. Forest Ecol. Mgmt. 6:217-244.
- Keresztesi, B. 1988. Black locust: the tree of agriculture. Outlook on
- Mebrahtu, T. and J.W. Hanover. 1989. Heritability and expected gain estimates
for traits of black locust in Michigan. Silvae Genetics 38:125-130.
- Miller, R.O., P.D. Bloese, and J.W. Hanover. 1987. Black locust: a superior
short-rotation intensive culture species for biomass production in the Lake
States. Inst. of Gas Technology, 11th Ann. Meeting on Energy from Biomass and
Wastes, March 16, 1987, Orlando, FL.
- Prentice, R.A. 1987. The effects of genotype and various cultural factors on
vegetative propagation of black locust (Robinia pseudoacacia L.). MS
Thesis, Michigan State Univ, East Lansing.
- Smith A.L, C.L. Campbell, M.P. Diwakar, J.W. Hanover, and R.O. Miller. 1989.
Extracts from black locust as wood preservatives: A comparison of the methanol
extract with pentachlorophenol and chromated copper arsenate. Holzforschung
*This research was supported by the Michigan State University/USDA:CSRS Eastern
Hardwood Utilization Research Special Grant Program, Grant no. 85-CRSR-2-2604
||Fig. 1. Black locust wood is useful for lumber, paper pulp, posts, and
fuel. This clone growing in Hungary is straighter than most trees in North
America, where borer insects and heredity typically produce crooked trunks.
||Fig. 2. Black locust leaves are high in protein, and the new growth of dense plantings such as this can be harvested for livestock feed with conventional hay-cutting equipment. The stipular thorns on new growth do not become sharp until the stem turns woody.
Fig. 3. Field plots for investigating forage production were sown in
1988. Planting densities from 40,000 to 1,000,000 per hectare, seed sources,
cutting heights, and harvest times are under study.
||Fig. 4. This provenance/progeny test plantation in Michigan containing over 400 half-sib families was established in 1985. The first trees bloomed in 1987, in three years from seed. Seed pods are visible on the tree in the center.
Fig. 5. Black locust has been propagated by tissue culture from various
plant organs of seedlings and young or mature trees.
Last update October 2, 1997